Known integrated drive generators utilize a differential coupled between a prime mover and a main generator. A hydraulic pump-motor assembly known as a "hydraulic log" and including two positive displacement machines alternatively usable as pumps or motors is coupled between the prime mover and a compensation shaft of the differential to accomplish speed trimming to drive the main generator at constant speed. Such integrated drive generators have high reliability and work well for their intended purpose. However, the high cost of the hydraulic log is undesirable.
An alternative electro-mechanical arrangement for providing a constant speed drive generating system is disclosed in Baker, U.S. Pat. No. 4,694,187. This generating system utilizes a mechanical differential also coupled between the prime mover and the main generator. A power converter having a rectifier and inverter is electrically connected between the main generator output lines and a variable speed generator coupled to the compensation shaft of the differential. The system controls the converter having a rectifier and inverter to control trimming power. Such a control requires complex electrical controls to provide proper trimming power which can be expensive. Also, it is necessary to provide proper matching between rectifier and inverter circuitry and controls therefor.
The present invention is directed to overcoming one or more of the problems as set forth above.